The September 1992 to May 1993 timetable has off-peak departures from both Newcastle and Sunderland every 15 minutes at 00, 15, 30 and 45.
Between around 1000 and 1630 most stoppers extended to/from Gateshead Metro Centre.
From Newcastle the 00 was to Middlesbrough with some starting back from Carlisle or the Metro Centre. The rest terminated at Sunderland. The 30 departure came through from Hexham and, like the 00 called only at Heworth.
The 15 and 45 were all stations to Sunderland and came from the Metro Centre.
In the other direction the 00 came from Middlesbrough until 1100, after which the Boro service was the 30 departure to Newcastle. Most went to Hexham with one or two to Carlisle. The 00 and 30 were the fast services calling at Heworth. The ones starting at Sunderland projected to Metro Centre, Hexham or Carlisle in a seemingly random order.
The 15 and 45 were stoppers and generally went to Metro Centre in the daytime.
During the evening a 20 minute frequency was run until 2300, mainly between Newcastle and Sunderland calling at all stations, with just the odd one to/from Middlesbrough.
Sundays were half-hourly all stations and all starting or terminating in Newcastle. Approximately one every two hours extended to/from Middlesbrough.
Notables were the 0700 from Sunderland which started at Seaham and on Monday to Friday continued to Morpeth, 0840 Sunderland to Newcastle all stations which started at Nunthorpe, the 1300 from Sunderland which continued via Carlisle and the Cumbrian coast to Preston and the 2200 Sunderland to Newcastle which had come from Liverpool Lime Street.
Two other morning peak journeys also started at Seaham.
In the opposite direction the 0655 (Saturday) or 0700 (Mon-Fri) from Newcastle went through to Liverpool and the 1030 to Heworth and Sunderland had begun its gruelling journey in Barrow-in-Furness at 0615!
When I first worked in Leeds circa 1996 the 0618 Leeds to Newcastle ran via Middlesbrough and the Durham coast and served all stops from Sunderland to Newcastle; it would have hit Sunderland at about 0845-0850.
My July 1990 Tyne and Wear guide to Sunderland has the Monday to Saturday daytime and evening frequencies the same, i.e. 15 and 20 minutes respectively, but Sundays are only hourly. Being a local TW guide it doesn't show where anything went before or after Newcastle and Sunderland.
I've attached photos of the Monday to Saturday pages for September 1992 to May 1993 below, hopefully they're readable;